Predetermined torque release wrench

ABSTRACT

A predetermined torque release wrench comprises a tubular handle member, a torque transmitting arm pivotally connected to the front end of the handle member and a leaf spring having an arcuate shape in cross section. The leaf spring is so arranged that its concave surface is in faced relationship with the free end of the arm. One of the ends of leaf spring is fixed on a support block positioned in the rear portion of the handle member and the other end is engaged by the free end of the arm.

United State's Patent A 1 91 l Kobayashi Jan. 22, 1974 [54] PREDETERMINED TORQUE RELEASE 2,962,918 12/1960 Van Hoose 8l/52.5 x 2,371,901 3/1945 Livermont 81/525 WRENCH [75] Inventor: Seiichiro Kobayashi, Tokyo, Japan [73] Assignee: Kabushiki Kaisha Nakamura Seisakusho, Tokyo, Japan [22] Filed: Dec. 11, 1972 [21] Appl. N0.: 313,757

521 us. (:1. ..s1/s2.4 [51] Int. Cl. B25b [58] Field of Search 81/524, 52.5

[56] References Cited UNITED STATES PATENTS 2,472,659 6/ l949 Greer 8l/52.4 R 2,205,510 6/1940 Wolfram 81/524 R Primary Examiner-James L. Jones, Jr. Attorney, Agent, or Firm-Harold L. Stults 57 ABSTRACT A predetermined torque release wrench comprises a tubular handle member, a torque transmitting arm pivotally connected to the front end of the handle member and a leaf spring having an arcuate shape in cross section. The leaf spring is so arranged that its concave surface is infaced relationship with the free end of the arm. One of the ends of leaf spring is fixed on a support block positioned in the rear portion of the handle member and the other end is engaged by the free end of the arm.

4 Claims, 5 Drawing Figures 16:13 20'E212s 2? 26 y N 24 PREDETERMINED TORQUE RELEASE WRENCH This invention relates to a torque wrench for tightening a load, such as a bolt or nut with a predetermined torque.

I-Ieretofore, the applicant has proposed a torque wrench comprising a torque transmitting member, a handle member and leaf springs which interconnect said member and resist the movement of the torque transmitting members, untila desired amount of torque is applied thereby, said leaf springs being arcuate in cross section.

One of disadvantages of the torque wrench of this type is that the amount of torque to be applied to a bolt or nut can not be adjusted since the leaf springs are fixedly secured at their one ends to the torque transmitting member and at the other ends to the handle member. The other disadvantage is that during the application of the torque to the bolt, the leaf spring would tend to twist and this tendency would produce an improper torque.

Accordingly, it is an important object of the present invention to provide a torque wrench in which an amount of torque to be applied by the wrench may be adjusted and the adjusting operation may be easily performed.

Another object is to provide a torque wrench in which a leaf spring resisting the movement of a torque transmitting armvduring the application of the torque to a bolt or nut by the wrench has no tendency to twist.

A further object is to provide a torque wrench which is simple in construction and is inexpensive to manufacture.

' These and'other objects and advantages .of the present invention will become apparent from the following detailed description of a preferred embodiment thereof, when taken in conjunction with the appended drawings wherein: I

FIG. 1 is a top plan view of a torque wrench embodying the present invention, which view is partly shown in section; I

FIG. 2isa view similar to FIG; 1 but showing the torque wrench in operative position;

FIG. 3 is a side elevational view of the'torque wrench;

FIG. 4 is a vertical sectional view taken on line IV-IV of 'FIG. '1; and

FIG. 5 is a vertical sectional view taken on line V-V of FIG. 1.

Referring to the drawings, the torque wrench according to the present invention comprises a torque transmitting arm and a tubular handle member 11 which is open at both ends. The tubular handle member 11 has a flattened portion 12 and a cylindrical portion 13. The arm 10 extends through the front open end of the handle member 11 into its flattened portion 12 and is pivotally connected to the handle member 11 by means of a pivot pin 14. The arm 10 is formed at its front end with a wrench head 15 of any desired type and at its rear end with a projection 16 engaging the extending front portion of a leaf spring 17 for resiliently resisting counter-clockwise rotation of the free end of the arm 10 as torque is applied to a bolt by the wrench head 15.

The leaf spring 17 is of an arcuate shape in cross section and is so arranged that the concave surface is in faced relationship with the projection 16 of the arm 10. A support block 18 is slidably disposed within the cylindrical portion 13 of the handle member 11 and is formed at its front end with a recess 19 having the surface on which the outer convex surface of the spring 17 is seated. The rear end portion of the leaf spring 17 is sandwiched between the recess 19 and a spring retainer 20 disposed in the recess 19 and is fixedly secured on the support member 18 by means of a set screw 21 extending through the spring retainer 20 and through the leaf spring 17 into the support block 18. The support block 18 is formed onits periphery with an axially extending slot 22 in which a guide pin 23 extending through the handle member 11 is received, to prevent it from rotating within the cylindrical portion 13 but permit axial movement of the support block 18 relative to the handle member 11. An adjusting screw 24 is disposed adjacent the other open end of the handle member within the cylindrical portion 13 and comprises a head 25 having an annular groove 26 formed on its periphery and an externally threaded portion 27 formed integrally with the head. The threaded portion 27 of the adjusting screw 24 is threadably engaged with a threaded bore 28 formed axially of the support block 18. A stopper screw 29 extending through the handle member 11 is received in the annular groove 26 on the head 25 to prevent the adjusting screw 24 from moving axially as it is rotated relative to the handle member 11. With this arrangement, I otation of the screw 24 will effect axial movement of the support block 18 relative to the handle member ll'and the screw 24 will also serve as means for connecting the support block to the handle 11.

In operation, the head 25 is engaged with, for example, a bolt 32 as shown in FIGS. 1 and 2 and the handle member I 1' is urged in a clockwise direction from its position of FIG. I. As torque is applied to the bold 32, the arm 10 tends to rotate in a counter-clockwise direction from its position of FIG. I. This tendency is resisted by the force of the leaf spring 17 acting against the free end of the arm 10. When, however, the torque being applied by the head 15 reaches a predetermined value, the leaf spring 17 will be subjected to buckling at point adjacent the end face of the support block 18, as shown in FIG. 2 and the arm 10 will suddenly pivot in a counter-clockwise direction about the pivot pin 14 until a portion of the arm abuts with the interior of the handle member 11 at point 31, as shown in FIG. 2. It will be understood that the arcuate leaf spring is characterized by that when the buckling of the spring occurs, the bending moment of the spring suddenly decreases. Thus, the sudden decrease of the bending moment causes the arm to strongly knock against the interior of the handle member to produce a sharp click.

It should be understood that the amount of torque applied to the bolt 32 before the arm 10 undergoes counter-clockwise movement is adjusted by varying the buckling load of the leaf spring 17. Such a variation of the buckling load may be accomplished by changing a distance from the fixed end of the spring 17 to the engagement of the extending portion of the leaf spring 17 with the projection 16 of the arm 10. As the adjusting screw 24 is rotated, the support block 18 is moved relative to the handle member 11 so that said distance will be changed to vary the amount of torque to be applied to the bolt by the torque wrench.

- From the foregoing-description, it will be apparent that there has been provided an effective and useful torque wrench which may be readily adjusted to vary the amount of torque to be applied to the bolt or nut to any desired value. It will be further apparent that there has been provided a torque wrench of the abovementioned type in which when the amount of the torque being applied to the bolt or nut reaches a predetermined value, the reliable buckling of the leaf spring occurs without any tendency to twist because of abutment of the free end of the pivoted arm with the concave surface of the extending portion of the leaf spring.

Having fully described this invention it is to be understood that it is not to be limited to the details herein set forth and therefore, various modifications and changes may be made thereto without departing from the spirit of the invention or the scope of the following claims.

I claim:

1. A predetermined torque release wrench comprising a tubular handle member having open ends, a torque transmitting arm extending through one open end of said handle member into the interior of said handle member and having at its one end a wrench head, means for pivotally connecting said arm to said handle member, a support block positioned in said handle member, and a leaf spring having an arcuate shape in cross section and an end fixedly secured on said support block and an extending portion engaging the free end of said arm, said leaf spring being so arranged that its concave surface is in faced relationship with the free end of said arm.

2. A wrench as set forth in claim 1 wherein said support block is slidably disposed in said handle memer, and which includes means for axially moving said support block relative to said handle member to change a distance from the fixed end of said leaf spring to the engagement of the extending portion of said spring with the free end of said arm.

3. A wrench as set forth in claim 2 which includes means for preventing said support block from rotating during axial movement of said support block.

4. A wrench as set forth in claim 2 wherein said means for axially moving said support block relative to said handle member includes a threaded bore formed axially of said support block and an adjusting screw rotatable without axial movement and having an externally threaded portion threadably engaged with said threaded bore. 

1. A predetermined torque release wrench comprising a tubular handle member having open ends, a torque transmitting arm extending through one open end of said handle member into the interior of said handle member and having at its one end a wrench head, means for pivotally connecting said arm to said handle member, a support block positioned in said handle member, and a leaf spring having an arcuate shape in cross section and an end fixedly secured on said support block and an extending portion engaging the free end of said arm, said leaf spring being so arranged that its concave surface is in faced relationship with the free end of said arm.
 2. A wrench as set forth in claim 1 wherein said support block is slidably disposed in said handle memer, and which includes means for axially moving said support block relative to said handle member to change a distance from the fixed end of said leaf spring to the engagement of the extending portion of said spring with the free end of said arm.
 3. A wrench as set forth in claim 2 which includes means for preventing said support block from rotating during axial movement of said support block.
 4. A wrench as set forth in claim 2 wherein said means for axially moving said support block relative to said handle member includes a threaded bore formed axially of said support block and an adjusting screw rotatable without axial movement and having an externally threaded portion threadably engaged with said threaded bore. 